This Nonprovisional application claims priority under 35 U.S.C. § 119(a) to patent Application No. 2002-333704 filed in Japan on Nov. 18, 2002, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention pertains to a sensor for detecting the entry of object(s) into overlapping zone(s) at which projected light optical path(s) of light irradiated from light-projecting component(s) overlap received light optical path(s) of light incident on light-receiving component(s).
2. Description of the Related Art
Conventional sensors include automatic door sensors having the ability to vary the protected zone for the detection of persons traveling therethrough, as disclosed, for example, in Japanese Patent Application Publication Kokai No. H3-55381 (1991).
In this automatic door sensor, a light-projecting component and a light-receiving component are disposed above an automatic door. A two-piece rotatable mirror is employed as a reflecting mirror to reflect light irradiated from the light-projecting component. The reflecting mirror splits the light irradiated from the light-projecting component into two beams which irradiate the floor, forming a first zone proximate to the door, and a second zone which is removed (distant) from this first zone. Furthermore, a two-piece rotatable reflecting mirror is provided at the light-receiving component on which reflected light from this first zone and this second zone is incident, and reflected light beams from the first zone and the second zone are respectively received by the light-receiving component.
In this automatic door sensor, because the light-projecting and light-receiving components respectively employ rotatable reflecting mirrors, it is possible, through adjustment of the rotational angles of these reflecting mirrors, to simultaneously relocate the first zone and the second zone.
Now, it is generally the case with automatic door sensors that the density of the light irradiated from the light-projecting component will be highest near the automatic door sensor, and will decrease as one goes outside of that region and approaches regions peripheral thereto. Furthermore, if the distance between the light-projecting component and the light-receiving component arranged therein is varied, then, by holding the density of the light irradiated from the light-projecting component constant, the density of the light irradiated from the light-projecting component will decrease as the distance between the two is increased.
Using the automatic door sensor disclosed in Japanese Patent Application Publication Kokai No. H3-55381 (1991) as an example to illustrate this fact, the optical path length of the light beam arriving at the light-receiving component after reflection from the (peripheral) second zone will be longer than that of the light beam arriving at the light-receiving component after reflection from the first zone (near the light-projecting component). For this reason, while it is possible with this automatic door sensor to vary protected zones so as to form arbitrary protected zones (first zone(s) and second zone(s)), it is not possible to carry out a detection of objects entering protected zones such that equivalent light density, i.e., optical sensitivity, is used for detection thereof across all protected zones. For this reason, taking detection in the first zone as the reference, it will sometimes be the case that the low light density and low optical sensitivity in the second zone will prevent detection thereat. Alternatively, taking detection in the second zone as the reference, the high light density and high optical sensitivity in the first zone will sometimes cause faulty operation such that objects not intended for detection, e.g., paper lying on the ground or the like, are detected thereat.
In order to solve one or more of the aforementioned problems, it is therefore an object of the present invention to provide a sensor having an ability to vary protected zone(s) at which detection of person(s) traveling therethrough and/or other such object(s) are detected, and for carrying out the detection of object(s) entering protected zone(s) such that the detection thereof is carried out with equivalent optical sensitivity across all protected zones despite any varying of protected zone(s).